Pesticides from water, loss

Sorption and Desorption Processes. Sorption is a generalized term that refers to surface-induced removal of the pesticide from solution it is the attraction and accumulation of pesticide at the sod—water or sod—air interface, resulting in molecular layers on the surface of sod particles. Experimentally, sorption is characterized by the loss of pesticide from the sod solution, making it almost impossible to distinguish between sorption in which molecular layers form on sod particle surfaces, precipitation in which either a separate soHd phase forms on soHd surfaces, covalent bonding with the sod particle surface, or absorption into sod particles or organisms. Sorption is generally considered a reversible equdibrium process. 

Sparks DL (ed) (1986) Soil physical chemistry. CRC Press, Boca Raton, Florida Sparks DL (1989) Kinetics of soil processes. Academic Press, San Diego Sparks DL, Huang PM (1985) Physical chemistry of soil potassium. In Munson RE (ed) Potassium in agriculture, ASA, Madison, Wisconsin, pp 201-276 Sparks DL, Jardine PM (1984) Comparison of kinetic equations to describe K-Ca exchange in pure and mixed systems. Soil Sci 138 115-122 Spencer WF, Cliath MM (1969) Vapor densities of dieldrin. Environ Sd Technol 3 670-674 Spencer WF, Chath MM (1973) Pesticide volatilization as related to water loss from soil. J Environ Qual 2 284-289... 

Despite the advantages, there is concern over the use of such containment methods because the fate of pesticides put into such sites is not well known ( 1 ). One such fate process is volatilization from the disposal site. Organophosphorus pesticide volatilization from water and soil is relatively unlnvestlgated, and if this route of loss occurs to an appreciable extent from disposal sites, a local respiratory hazard may exist. 

Experimental and predicted volatilization rate constants for the five pesticides are listed in Table II. It should be noted that, despite low H values for the pesticides, experimental volatilization rates for diazlnon and parathlon are fairly rapid from water under the conditions of our tests (t> of 4.2 and 9.6 days, respectively). When compared to their hydrolysis rate constants (Table I), volatilization can be seen to be a more important route of loss than hydrolysis for diazlnon, parathlon, and methyl parathlon. The relative volatilization rates reported here for diazlnon and parathlon are in good agreement with those reported by Lichtenstein (14). 

It should be noted that hydrolysis of these pesticides is expected to occur simultaneously with volatilization for the pesticides studied (Table I). Over a 7 day experiment, however, only malathion and mevlnphos would be expected to hydrolyze to a significant extent. We determined the loss rate of mevlnphos to be 0.0016 0.0002 hr l (tjj = 18 days), and of malathion to be 0.011 0.001 hr-1 (t j = 2.6 days) at 22 2°C, at pH 8.2+0.2 for a model evaporation pond by daily sampling of duplicate pesticide solu-Xlons (covered to prevent volatilization) for 7 days and plotting log concentration versus time. For both of these pesticides, then, degradation was a much more important route of pesticide loss from water than volatilization. The relatively slow loss rate of the other pesticides could not be determined in our 7 day... 

A simple environmental chamber is quite useful for obtaining volatilization data for model soil and water disposal systems. It was found that volatilization of low solubility pesticides occurred to a greater extent from water than from soil, and could be a major route of loss of some pesticides from evaporation ponds. Henry s law constants in the range studied gave good estimations of relative volatilization rates from water. Absolute volatilization rates from water could be predicted from measured water loss rates or from simple wind speed measurements. The EXAMS computer code was able to estimate volatilization from water, water-soil, and wet soil systems. Because of its ability to calculate volatilization from wind speed measurements, it has the potential of being applied to full-scale evaporation ponds and soil pits. 

Bioaccumulatlon of some pesticides (fenitrothion, aminocarb, permethrin) with real or potential application in forestry in Canada has been examined in laboratory experiments using larval rainbow trout and common duckweed. Bioaccumulation of an aromatic hydrocarbon, fluorene, has also been examined since some commercial formulations employ hydrocarbon solvents. Laboratory exposures of fish or plants were carried out by placing the organisms in dilute aqueous solutions of C labelled pesticide or hydrocarbon, and by measuring transfer of radioactivity from water to fish or plants. After transfer of fish or plants to untreated water, loss of radioactivity was measured similarly. These measures allowed calculation of uptake and depuration rate constants which were used to predict residue accumulations under various exposure conditions. Predicted residue accumulations agreed substantially with other predictive equations in the literature and with reported field observations. 

Evidence was obtained recently that pesticide vapors may enter the air by still another mechanism, involving plant circulation and water loss (57). Rice plants were found to efficiently transport root-zone applied systemic carbamate insecticides via xylem flow to the leaves, eventually to the leaf surface by the processes of guttation and/or stomatal transpiration, and finally to the air by surface volatilization. Results from a model chamber showed that 4.2, 5.8, and 5.7% of the residues of carbaryl, carbofuran, and aldicarb, respectively, present in rice plants after root soaking vaporized within 10 days after treatment. The major process was evaporation of surface residues deposited by guttation fluid. 

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